The present invention generally relates to image production using a radiosity method which is one of arts for obtaining the irradiance of the body surface in a tertiary dimension space in a computer graphic field.
In recent years, the radiosity method noteworthy in real image producing art is an algorithm which assumes the body surface in the tertiary dimension space as diffuse surface, calculating the irradiance values of the body surface, considering interreflection. The radiosity means energies per unit time, unit area in the radiating operation of, by light receiving faces, the light received directly from a light source and the light received indirectly by the interreflection. The radiosity is often mixed with illumination, because it is equal to the radiation, in terms of unit, in the light engineering. (In the present patent, the radiosity is used in the mixture with the illumination.) The calculation art is a step of dividing the body surface into mesh shaped elements as in the general numeral calculation and obtaining the radiation illumination, considering form-factors with respect to the elements by one. It is a step lose to a boundary element method in terms of this fact.
An article, Goral, Cindy M., Torance, Kenneth e., Greenberg, Donald P., "Modeling The Interaction of Light between Diffuse Surface", Computer Graphics (SIGGRAPH'84 proceedings), vol. 18, no. 3, pp213-222, July 1984, has known the algorithm generally for the first time in the field of computer graphics.
A big difference is in that an intersection processing (hidden face processing) used in the field of the computer graphics conventionally is applied as a step of effecting a processing operation of taking the complexes into consideration with the form of the body of the calculation object and the positional elation between the bodies being very complex. Non-linear elements are added because of the above described complex. Judgment is required to be made as to whether lights from the light source or the reflection lights from a certain faces reaches the bodies of the target, namely, a body to be covered exists between them. The intersection test processing operation is provided to effect the processing operation.
In the intersection test processing operation, the processing time is largest during he radiosity calculation processing operation. The high speed of the intersection test processing operation is the most useful effect in the higher sped operation of the radiosity calculation.
In an article, Cohen, Michael F., Greenberg, Donald P., "The Hemi-Cube: A radiosity Solution for Complex Environments factor", Computer Graphics (SIGGRAPH'85 Proceedings), vol. 19, no.3, pp 31-40, July 1985, a Hemi-Cube method applying z buffer method as one step of the higher speed of the intersection test is announced for the fist time. In addition to the Hemi-Cube method, there are many articles about the Henmi-Cube method.